1. Field of the Invention
This invention is generally directed to flow control devices for use in water wells and in particularly to a downhole flow controller for use in recharge, injection and aquifer storage recovery wells wherein the VoSmart (a Variable Orifice Selective Monitored Artificial Recharge Throttle) valve continuously regulates the flow of water during periods of recharging. During recharging the water in the column or drop pipe is controlled to prevent air from being entrained or trapped in the fluid flow and carried into the aquifer. Entrained air can adversely affect the recharge efforts, through air-fouling, bio-fouling and calcite formation, by blocking the flow of water into the aquifer.
2. History of the Invention
Many water districts and communities have realized the need and value of maintaining the water level and storage capacity of the aquifers that provide their drinking water. Further due to the high demand and to the variability of supply and demand, it is logical that an adequate reserve capacity of the water storage facilities be maintained to provide for extended peak demands, droughts and explosive growths in new customers. Reserve storage capacity to provide for these events in capital facilities is prohibitively expensive to construct and more difficult to justify, therefore capital facilities typically lag behind demand.
In an effort to reduce these capital facility costs, water resource engineers have become interested in the concept of replacing or storing large volumes (banking) of treated water in aquifers during periods of the year when both water and facility capacity are available to supply water required to recharge aquifers. The concept replacing the water pumped from the aquifer or seasonal storage is called Aquifer Storage Recovery or ASR. This scenario is an alternative to conventional expansion of water supply, treatment, distribution and storage capital facilities is quite cost effective in areas where it is technically feasible. In general, a well based system or one that is partially well based is a system that the wells can be used for both recharge and recovery. In recovery, the water may require only disinfection. Recharge wells may be through existing wells or through dedicated recharge wells.
In addition to reduction in facilities expansion costs, other advantages favor recharge technology. In coastal areas reduced levels in aquifer water may permit the intrusion of salt water which can result in the destruction of the fresh water supply. In these areas, a mound of recharged fresh water is placed, through balanced flow control, in the aquifer forming a uniform curtain or barrier between the salt water and the fresh water, effectively preventing salt water intrusion. At times, this volume of water can be used to meet seasonal peak demands.
Such storage and water resource techniques have proven extremely advantageous and cost effective in areas where declining ground water levels have reduced or left wells nearly non-productive.
Another application of this type of device is the use in ground water remediation. In areas where existing ground water supplies are threatened or have been contaminated flow control devices are effective in managing an effective program. Once the water is extracted and treated, this type of flow control device is able to balance the flow in a series of recharge wells to provide a uniform curtain of water, placing the water in the aquifer evenly and uniformly.
Well recharging is also effective where substantial reserves are necessary to improve system reliability in the event of a catastrophic loss of a primary water supply or in communities where strategically located reserves are required to ensure an adequate balance in system flows during peak demand.
Although there are obvious benefits to be obtained from recharging existing production water wells or in constructing new water storage recovery wells, in many applications problems have been encountered with air entrapment in the recharge water causing air binding of the aquifer. Air binding effectively decreases the permeability of the aquifer, thereby decreasing the effectiveness of the recharging operations. Such air entrapment is most frequently encountered in areas or localities where one or more of three conditions exist. These conditions may be encountered when: (1) the recharge water must drop a considerable distance from the well head to the static water level; (2) when the recharge flow is relatively low; and (3) where the specific capacity of the well is relatively high. The foregoing conditions have resulted in the cascading of water in the column or drop pipe, thereby entrapping large quantities of air which is carried into the well and outwardly into the aquifer. The entrapped air can effectively plug or seal the aquifer, a condition known as air fouling, resulting in substantially lower permeability and storage capacity. The answer to mitigating this problem is to pump the well, thereby restoring a portion of the lost capacity.
There have been flow control devices developed by the oil and gas industry, such controllers are not suitable for use in controlling cascading in recharge, injection or aquifer storage recovery wells. One alternative used to mitigate the air entrainment involves the use of multiple small injection tubes to place the water in the aquifer. Such alternative is possible in wells using large diameter well casing and well screens. This system is costly and generally not suitable for retrofitting existing wells.
The invention is directed to a downhole flow control device for continuously regulating the flow of water during recharge, injection or aquifer storage recovery. During recharge, the flow is controlled to prevent cascading water which would otherwise lead to air-fouling or aquifer plugging through air entrapment. The embodiment includes two concentric cylinders or tubular members, one of which has flow control ports, the other is connected to and selectively moved by the hydraulic actuator section, thereby setting the flow through the ports by varying their size.
The inner tubular member with the control ports is stationary and the outer tubular member is moved vertically by hydraulic pressure in the double acting hydraulic actuator section. The hydraulic actuator is controlled through two capillary tubes from the well head by a solenoid or manually operated three-position, four-way control valve in series with a flow control valve. The hydraulic pressure is supplied by an electrically driven pump. Speed of operation is set by adjusting the hydraulic fluid flow control valve manually or automatically. The solenoid valve may be controlled locally or by a Supervisory Control and Data Acquisition (SCADA) system from a remote location.
The device is connected in one of three ways: first, by being installed below a vertical turbine pump and above a foot valve, a configuration that is set up for co-generation during recharge; second, being installed above a submersible pump and check valve; and third, being connected to the bottom end of the injection pipe with the device closed at its lower end.
In dual purpose wells used for both water production and recharge (also known as aquifer storage and recovery, or ASR, wells), the device is installed at the base of the pump column, just below the pump bowls and above the foot valve/strainer. This application is best suited for co-generation during recharge, the pump is rotated during recharge and the motor becomes a generator producing electricity. A second application is with the device installed above a submersible pump and check valve. During recharge the pump and motor are stationary. In single purpose recharge or injection wells, the device with a closed lower end, is connected to the bottom of the drop pipe and set near the top of the well screen.
The primary objective of the device is to produce downhole flow control for use with recharge, injection and aquifer storage recovery (ASR) wells wherein the flow of the recharge water is facilitated and controlled in order to eliminate a significant amount of air-fouling or well plugging through air binding form air entrapment.
Another objective of the invention is to provide downhole flow control for recharge, injection and ASR wells which are designed to be incorporated within existing or new wells in order to reduce air entrainment which is normally associated with recharge operations.
It is also an objective of this invention to provide a simple, durable and cost effective flow control for regulating the flow hydraulically, while monitoring a flow measuring device (meter) which assures a desired well flow that can be adjusted to meet the specific static and operational pressures that are encountered or anticipated in a variety of environments.
It is a further objective of this invention to provide downhole flow control for preventing air binding in recharge, injection and ASR wells wherein minor adjustments to flow may be selectively regulated from the well head.
The term xe2x80x9centrained airxe2x80x9d is a technical term describing the action taking place in a waterfall. In this case, the waterfall is inside the drop pipe of an artificial storage and recovery (ASR) or recharge well. This can have detrimental effects and can nearly stop the flow of recharge water. It is therefore another object of this invention to prevent entrained air from interfering with the flow of recharge water.
Supervisory Control and Data Acquisition (SCADA) control of the device may take many forms, depending on the degree of complexity desired. A minimum system may consist of a pressure sensor at the well head as a control device to maintain a minimum pressure and a flow meter. The pressure sensor is used to maintain a positive water pressure at the well head of 5-10 PSI minimum. The water meter is for monitoring and controlling water flow rate through the system and is controlled by a valve. The pressure sensor is monitored by the SCADA system with appropriate electronic signals sent to the power unit for incremental adjustments to the power unit. The power unit controls the hydraulic solenoid and then to the valve by using hydraulics and connecting fluid and hoses. A unique feature of the hydraulic power unit is a pilot operated check valve configured according to the invention. This feature hydraulically locks hydraulic fluid used to control the check valve in position when the solenoid valve is in the center position or when the power unit is shut off.
According to another aspect of the invention, the sequence of starting up the system is to start with the valve in the closed position, then fill the drop pipe with water, and then pressurize connecting piping. This allows the air inside the drop pipe to escape through an air vacuum valve at the well head. The valve may now be positioned manually or by SCADA control to reach and maintain a desired flow rate.
During times when the valve is not being adjusted, the power unit is normally powered down or placed in a stand-by mode by the SCADA system. When the valve needs to be adjusted, the power unit is turned on, adjustments made to set or reset the water flow by monitoring the flow meter with the SCADA system.